Abstract: This paper deals with the optimization of the process conditions for the enzymatic hydrolysis of Undaria pinnatifida protein using response surface methodology (RSM). With this aim in mind, after selection of an appropriate enzyme, the effects of hydrolysis time, pH, hydrolysis temperature, substrate concentration and enzyme dosage on the degree of hydrolysis and the antioxidant activity of hydrolysates were investigated using RSM based on one-factor-at-atime experiments. The optimized hydrolysate was compared with the natural antioxidant ascorbic acid and the synthetic antioxidant butyl hydroxyanisole (BHA) in regard to their antioxidant activity. The results showed that protamex was the best enzyme for the hydrolysis of U. pinnatifida protein. The optimal conditions that provided ferrous ion-chelating ability and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity were determined as follows: hydrolysis time, 8.1 h; pH, 7.0; hydrolysis temperature, 50 ℃; substrate concentrate, 15 g/L; and enzyme dosage, 0.2% (0.3 AU/g). Under these conditions, the rate of chelation of ferrous ion by the hydrolysate was up to 88.58%, which was significantly higher than that by 0.01% ascorbic acid and BHA (P < 0.05). However, in terms of DPPH free radical scavenging percentage (59.22%) and reducing power, the hydrolysate was inferior to 0.01% ascorbic acid and BHA (P < 0.05).

Key words: Undaria pinnatifida, enzymatic hydrolysis, response surface methodology, antioxidant activity, hydrolysis degree